A centrifugal blower is used for a vehicle air conditioner, for example. In the vehicle air conditioner, air is drawn from a single suction port and is blown into plural outlets by the blower, and pressure loss is relatively large due to a bent air passage of an air conditioning duct. Therefore, a centrifugal blower of a pressure type is generally used as the blower for the vehicle air conditioner.
For example, a sirocco fan is described in JP-A-2003-35298, and a turbofan is described in JP-A-2003-269380. Furthermore, a centrifugal blower shown in FIG. 9 is described in JP-B2-3489221. The blower shown in FIG. 9 includes a boss portion 102 for fixing a motor 100, and a fan member 105 including a plate member (bottom plate) 104 for connecting plural blades 103. The bottom plate 104 is formed into a mountain shape which is lowered from a high center portion toward a peripheral portion.
In the blower of FIG. 9, the flow direction of air drawn from an axial direction is changed to radially outward by the bottom plate 104. Further, as shown in FIG. 10, air flows along the surface of the bottom plate 104. Therefore, the flow speed of air near the surface of the bottom plate 104 becomes larger, and the flow speed of upper side air far from the surface of the bottom plate 104 becomes smaller. Because the flow speed of air is different between the upper portion and the lower portion in a height direction of the bottom plate 104, the air streams at different portions collide and are disturbed. Accordingly, fan noise due to the disturbed air flow is generated.